1. Field of the Invention
This invention relates to industrial valves and more specifically relates to an improved packing assembly for use in gate valves to attenuate leakage about the gate.
2. Description of the Related Art
Gate valves are used in many industrial applications to selectively modify the flow rate of fluid through a pipe into which the gate valve is incorporated. Gate valves generally comprise a valve body having an opening the diameter of which approximates the diameter of the pipe into which the valve is incorporated, a valve seat associated with the opening and a solid gate plate which is vertically slidable within the valve body to selectively occlude the opening to control the flow of fluid through the pipe. The solid plate of the gate is typically structured with or attached to a valve stem or tubular spindle which is actuated in some manner, such as manually or electromechanically, to raise and lower the gate within the valve body. The particular construction and design of gate valves varies widely among manufacturers.
Most gate valves are specifically designed and constructed to provide sealing mechanisms which seal the valve body as completely as possible against fluid leaks. Complete sealing is particularly necessary when such valves are employed in industrial applications where toxic or otherwise environmentally harmful fluids are being processed. The primary focus of leakage is between the gate, the valve seat and the housing. A second area of concern for leakage is between the housing and the slidable gate, or the valve stem which operates to raise and lower the gate. Recognizing the need to seal the valve stem from leakage in many valve types, including gate valves, the patent literature is replete with patents which disclose packing or stuffing systems for valve stems.
Another area of concern, and that which is relevant to the present invention, is the prevention of leakage about the gate plate itself. Many gate valves have been designed to include a packing mechanism or system which encircles or extends about the gate to seal the flat surfaces and ends of the gate against leakage. Examples of such gate valve constructions are disclosed in U.S. Pat. No. 3,000,608 to Williams; U.S. Pat. No. 3,710,816 to Prince; U.S. Pat. No. 4,646,407 to Mayhew; U.S. Pat. No. 5,082,247 to Owens, et al.; U.S. Pat. No. 5,137,261 to Clifford; U.S. Pat. No. 5,205,317 to Neuerberg, et al.; U.S. Pat. No. 5,292,105 to Velimirovic; and U.S. Pat. No. 5,582,200 to Kimpel, et al.
Some of the gate valve constructions disclosed in the patent literature, for example U.S. Pat. No. 4,646,407 and U.S. Pat. No. 5,205,317, merely comprise the formation of a packing cavity in the valve housing into which an amount of packing material, such as braiding, is positionable. Other gate valves are constructed with a cavity formed into the upper surface of the valve housing into which an amount of braided packing material is positioned. The packing material is then compressed into the cavity and against the gate plate by means of a compression device or gland that also encircles the gate. Examples of such constructions are disclosed in U.S. Pat. No. 3,710,816; U.S. Pat. No. 5,082,247; U.S. Pat. No. 5,137,261 and U.S. Pat. No. 5,582,200. Both U.S. Pat. No. 3,000,608 and U.S. Pat. No. 5,292,105 disclose an arrangement where a packing box is provided for positioning above the top edge of the housing.
One inherent problem with known packing systems for gate valves is the fact that as the gate opens and closes over time, the packing loosens or shifts and leakage begins. This problem occurs in known packing systems because they are not structured to and cannot apply even pressure distribution about the surfaces and rounded corners of the gate plate to provide stability to the packing material and thereby prevent leakage. Known packing systems, therefore, last for a relatively short time. Once the packing begins to fail, the compression means or packing gland must be repeatedly tightened to reseal the gate and staunch the leakage. Additionally, there is some resistance among various industries to repeatedly tighten the compression means of the packing system; but certain industries, especially those processing or producing toxic or noxious fluids, are obligated to eliminate fugitive emissions from the system.
Therefore, it would be advantageous in the art to provide a packing system for a gate valve which is structured to provide even distribution of the packing material against the gate valve to avoid leakage about the gate plate and to extend the longevity of the packing system before further adjustment would otherwise be required.
In accordance with the present invention, a packing system for the gate plate of a gate valve is structured to provide even distribution of pressure to the packing material about the gate plate and to provide enhanced means of sealing the packing material from the environment external to the packing system to thereby eliminate leakage about the gate plate.
The packing system of the present invention generally comprises a sealing member which is configured with a slot to receive the gate plate of a valve therethrough. The sealing member is further configured to be positioned along the upper edges of a valve housing having a cavity formed in the top thereof in which packing material is positionable to surround the gate plate. The sealing member is sized and configured to extend over and contact the packing material in the cavity, and to provide an amount of compression to the packing material. The sealing member provides even distribution of compression pressure on the packing material because of its configuration.
The sealing member is further configured to accommodate an o-ring about a peripheral portion of the sealing member to seal the packing material in the cavity of the valve housing from the environment external to the cavity. The sealing member is also configured with a recess positioned about the slot through which the gate valve moves to retain an amount of sealing compound sufficient to seal the gate plate from leakage. The sealing member is preferably made from a non-metallic material which is suitable to provide comprehensive contact with the gate plate to eliminate leakage about the gate. Additionally, the sealing member serves as a guide for movement of the gate and provides support to the gate, thereby taking load and stresses off the packing material.
The packing system further employs a compression member or gland follower which, too, is structured with an elongated slot through which the gate plate moves. The gland follower is sized to extend over the sealing member to hold the sealing member in registration against the packing material. The gland follower is structured to provide selective adjustability to the amount of compression force applied to the sealing member. Thus, the gland follower is secured to an anchoring structure, such as a portion of the valve housing, so that the gland follower may be adjusted as needed. The gland follower may either be bolted to the anchoring structure or may be xe2x80x9clive-loadedxe2x80x9d through the use of spring-biased bolts.
The packing system of the present invention may further comprise a gasket which is positioned between the gland follower and the sealing member of the packing system. The gasket is configured with a slot through which the gate moves and the gland follower is structured to provide evenly distributed pressure to the gasket to assure a secondary sealing mechanism in the packing system of the present invention.
The configuration of the packing system of the present invention is particularly advantageous because the gate plate remains completely sealed throughout cycling of the valve or, in other words, throughout cycling between an open gate position and a closed gate position. In prior art gate valves, the configuration of the packing arrangement, and/or the machining of the parts, cannot provide complete sealing throughout cycling. These and other advantages of the present invention are illustrated further hereinafter.